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Mazda’s Hydrogen RX-8 RE

by Ron CoganAugust 27, 2021
Back to the future: Clean hydrogen power reaches beyond the fuel cell vehicles being explored today. Back in 2004, Mazda fielded its innovative RX-8 RE, a developmental rotary engine sports car that would drive on either hydrogen or gasoline fuel.

Hydrogen fuel cell vehicles have been in development for decades now as automakers strive to show how zero-emission, carbon-free hydrogen may be the ideal motor vehicle of the future. But focus hasn’t always been exclusively on hydrogen power generated through an electrochemical fuel cell. Some, like Mazda, showed us how internal combustion may present an easier and more seamless transition to the use of hydrogen. This automaker’s highest profile hydrogen project was the RX-8 RE that debuted 17 years ago, a model that could alternatively run on hydrogen or gasoline in its combustion rotary engine. Here, we present this article from the Green Car Journal archives as it was originally published in the Spring 2004 issue.

No stranger to hydrogen power, Mazda recognized some time ago that its rotary engine and clean hydrogen fuel operate quite well together. Green Car Journal editors understood this first-hand when driving the automaker’s developmental MX-5 Miata hydrogen rotary sports car a decade ago. These days, reinforcing Mazda’s enduring interest in what many consider  the ultimate environmental fuel is its latest developmental vehicle, which is based on the automaker’s acclaimed RX-8.

The Mazda RX-8 RE integrates Mazda’s Renesis hydrogen rotary engine, a lean-burn powerplant based on the automaker’s next-generation rotary engine launched earlier this year in the all-new RX-8 sports car. Even when running on conventional gasoline, the new Renesis features significant environmental improvement over previous generation rotary engines with better fuel economy and reduced emissions.

A rotary engine is especially well-suited for burning hydrogen since it uses separate chambers for induction and combustion. This overcomes the troublesome backfiring issues often faced when using hydrogen in piston engines.

In addition, Mazda says the separate induction chamber also provides  a safer temperature for the engine’s dual hydrogen injectors with their rubber seals, which can be damaged by the higher temperatures of conventional engines. Dual injectors are used in each of the engine’s twin rotor housings since hydrogen has an extremely low density, thus greater volumes of this fuel must be injected than gasoline.

Mazda’s RX-8 RE aims to provide a traditional driving experience as it achieves extremely low emissions with hydrogen. This is accomplished by integrating a dual-fuel approach that allows seamlessly operating on hydrogen as available, or gasoline when it’s not. This is important and reflects Mazda’s belief that a dual-fuel system promotes the use of hydrogen and a developing hydrogen refueling infrastructure. The RX-8 RE uses both a conventional gas tank and a high-pressure hydrogen tank.

The Renesis hydrogen engine features 210 horsepower when running on gasoline and 110 horsepower on less energy-dense gaseous hydrogen. Power is transferred to pavement through a five-speed manual transmission. Performance is enhanced with 225/45R18 tires over 18x8JJ alloys and double wishbone multi-link suspension front and rear, with stop- ping power supplied by four-wheel ventilated disc brakes.

An array of advanced technologies is used in the RX-8 RE to allow exploring their value for a future production hydrogen vehicle. These include an electric motor to boost engine torque at low rpm and an electric motor-assisted turbocharger, both used to improve acceleration at low revs. An idle-stop system turns the engine off when the car is stopped and then starts again automatically when the driver is ready to accelerate. Regenerative braking recovers energy during  deceleration and braking to charge the car’s 144-volt battery.

Other environmentally-conscious elements are incorporated into this high-profile hydrogen car, including water-based paint, interior parts made of plant-based plastics, optimized tires, and reduced overall weight. Reduced friction hub carriers and a fast-fill tandem master cylinder also serve to reduce brake drag.

This latest foray into the hydrogen world is a strong message that Mazda is giving hydrogen propulsion serious consideration, as it has for many years now. This automaker’s interest in hydrogen rotary power has been duly noted since the debut of its HR-X hydrogen concept car at the 1991 Tokyo Motor Show. A series of other hydrogen efforts have evolved at Mazda over the years including the HR-X2, MX-5, and Capella Cargo, all powered by hydrogen rotary engines, and the Demio FC-EV and Premacy FC-EV, powered by hydrogen fuel cells.

What has driven Mazda to pursue hydrogen fuel with such vigor for so long? A focus on environmental issues, of course, but also an apparent vision that this fuel stood at least a decent chance of coming out on top. That vision has now culminated in the Renesis hydrogen rotary engine and the outstanding RX-8 RE.

BMW, Ford, and now Mazda are raising the volume on the potential for using hydrogen in more conventional engines and not just in fuel cells. This adds additional motivation to create a hydrogen refueling infrastructure, promising to make things even more interesting as this alternative fuel is driven ever closer to the showroom in the years ahead.